TWI604439B - Noise cancellation device and noise cancellation method - Google Patents

Description

Noise canceling device and noise canceling method

The present invention relates to a noise canceling device, and more particularly to a noise canceling device and method having a mechanism for detecting a near ear and an ear.

In order to provide higher sound quality, active noise cancellation mechanisms are often added to the headphones to reduce the effects of ambient noise. In some techniques, active noise cancellation mechanisms often employ a single filter to generate noise cancellation signals. However, when the earphone is not in use (i.e., in an off-ear state), the system response of the active noise cancellation mechanism often varies greatly. In order to maintain the stability of the active noise cancellation mechanism, the above single filter can only use a circuit design with low noise cancellation effect but high stability. As a result, when the earphone is used (that is, in an on-ear state), it is not possible to provide a better noise canceling effect.

In some embodiments, the noise cancellation device includes a reverse noise filter circuit, an output circuit, and a detection circuit. The inverse noise filter circuit is configured to provide a corresponding one of the plurality of transfer functions to process the digital signal to generate a noise cancellation signal, wherein the plurality of transfer functions are different from each other. Output circuit for mixing noise cancellation In addition to the signal, reference signal and input signal to generate a mixed signal, and based on the mixed signal to generate a sound output signal, wherein the digital signal is associated with the sound output signal. The detecting circuit is configured to provide a corresponding one of the plurality of transfer functions by controlling the inverse noise filter circuit according to the comparison result of the first ratio and the first threshold, wherein the first ratio is a power pair digital signal of the mixed signal The ratio of power.

In some embodiments, the noise cancellation method includes the following multiple operations. The control reverse noise filter circuit provides a corresponding one of the plurality of transfer functions to process the digital signal to generate a noise cancellation signal, wherein the plurality of transfer functions are different from each other; the noise cancellation signal, the reference signal, and the input signal are mixed to generate a mixed signal, And outputting a sound output signal based on the mixed signal, wherein the digital signal is associated with the sound output signal; and controlling the reverse noise filter circuit to provide a corresponding one of the plurality of transfer functions according to the comparison result of the first ratio and the first critical value, wherein The first ratio is the ratio of the power of the mixed signal to the power of the digital signal.

In summary, the noise canceling apparatus and method provided in the present invention can analyze the near-ear state and the ear-off state by different setting methods to selectively use appropriate filters to improve the performance of the audio processing system.

100‧‧‧Noise elimination device

110, 115‧‧‧ analog to digital converter

120‧‧‧Backward noise filter circuit

130‧‧‧Output circuit

140‧‧‧Detection circuit

150, 155‧‧‧Audioelectric conversion device

160‧‧‧Reference signal generator

SO(t)‧‧‧Sound output signal

V(t), V2(t)‧‧‧ noise signal

E1(t), E2(t)‧‧‧ electronic signals

Y(n)‧‧‧ digital signal

H1(z), H2(z)‧‧‧ transfer function

122, 124‧‧‧ filter

126‧‧‧Switching circuit

NC(n)‧‧‧ Noise Cancellation Signal

SE‧‧‧Switch signal

132‧‧‧Operating circuit

134‧‧‧Digital to analog converter

136‧‧‧Electrical sound conversion device

X(n)‧‧‧ reference signal

M(n)‧‧‧ input signal

U(n)‧‧‧mixing signal

C(n)‧‧‧ digital noise signal

200‧‧‧ method

S210, S220‧‧‧ operation

S215, S230‧‧‧ operation

301~303‧‧‧band frequency filter

311~314‧‧‧Power estimation circuit

320‧‧‧Logical Circuit

U'(n), Y'(n), C'(n)‧‧‧ signals

Pu, Pn‧‧‧ power

Py, Px‧‧‧ power

T1‧‧‧Enable period

T2‧‧‧Cancellation period

S(z)‧‧‧ transfer function

The description of the present invention is as follows: FIG. 1 is a schematic diagram of a noise canceling apparatus according to some embodiments of the present invention; FIG. 2 is a schematic diagram of FIG. 1 according to some embodiments of the present invention. A flowchart of a method of operating a circuit; FIG. 3 is a diagram of FIG. 1 according to some embodiments of the present disclosure FIG. 4A is a circuit diagram of the detection circuit in FIG. 1 according to other embodiments of the present invention; and FIG. 4B is a diagram illustrating another embodiment according to the present disclosure. A waveform diagram of the reference signal as in Figure 4A.

Referring to FIG. 1, in some embodiments, the noise canceling device 100 is disposed on various electronic devices (eg, earphones) to reduce interference from ambient noise.

In some embodiments, the noise cancellation device 100 includes an analog to digital converter 110, 115, a reverse noise filter circuit 120, an output circuit 130, a detection circuit 140, a sound and electricity conversion device 150, 155, and a reference signal generator 160. .

In some embodiments, the acoustic-electrical conversion device 150 is disposed in the housing of the earphone and receives the sound output signal SO(t) and the noise signal V(t), wherein the sound output signal SO(t) passes through the transfer function S ( z) to the acousto-electric conversion device 150, and the transfer function S(z) is a transfer function between the electro-acoustic conversion device 136 to the acoustic-electric conversion device 150. The acoustic-electrical conversion device 150 converts the received signal into an electronic signal E1(t). In some embodiments, the acoustic-electrical conversion device 150 can be implemented by a microphone, but the present invention is not limited thereto.

The analog to digital converter 110 converts the electronic signal E1(t) to the digital signal Y(n). The reverse noise filter circuit 120 is coupled to the analog to digital converter 110 to receive the digital signal Y(n).

The reverse noise filter circuit 120 provides a transfer function H1(z) and One of the transfer functions H2(z) processes the digital signal Y(n) to generate a noise cancellation signal NC(n). For example, the reverse noise filter circuit 120 includes a plurality of filters 122 and 124 and a switching circuit 126. The switching circuit 126 selects the output of one of the filter 122 and the filter 124 as the noise canceling signal NC(n) according to the switching signal SE. Among them, the filter 122 provides a transfer function H1(z), and the filter 124 provides a transfer function H2(z). In some embodiments, the switching circuit 126 can be disposed between the analog to digital converter 110 and the inverse filter circuit 120, and the outputs of the filters 122 and 124 are coupled to the output circuit 130. In some embodiments, switching circuit 126 can be implemented by one or more switches. In some embodiments, switching circuit 126 can be implemented by a multiplexer circuit.

In some embodiments, filter 122 and filter 124 can be implemented by two separate filters. In other embodiments, filter 122, filter 124, and switching circuit 126 may be implemented by a single parameter adjustable parameter, wherein the parameters of the filter are adjusted according to switching signal SE to selectively provide a transfer function H1 (z ) or H2(z). The implementation of the reverse noise filter circuit 120 is merely an example, and the present invention is not limited thereto.

The output circuit 130 includes an arithmetic circuit 132, a digital to analog converter 134, and an electroacoustic conversion device 136. The operation circuit 132 is coupled to the switching circuit 126 to receive the noise cancellation signal NC(n), and mixes the noise cancellation signal NC(n), the reference signal X(n), and the input signal M(n) to generate the mixed signal U(n). ). In some embodiments, the arithmetic circuit 132 can be implemented by circuitry such as adders and/or synthesizers. In some embodiments, the input signal M(n) may be an audio signal output by the music source through the synthesizer and/or the amplifier. The digital to analog converter 134 converts the mixing signal U(n). Electroacoustic conversion device 136 is coupled to digital to class The ratio converter 134 outputs the converted signal U(n) as a sound output signal SO(t). In some embodiments, electroacoustic conversion device 136 can be implemented by a speaker.

In some embodiments, the detecting circuit 140 receives the digital signal Y(n), the digital noise signal C(n), the mixing signal U(n), and the reference signal X(n), and outputs the switching signal SE according to the signal. The switching circuit 126 is controlled. The above operation will be described in detail with reference to Fig. 2 which will be described later.

In some embodiments, the noise cancellation device 100 further includes an analog to digital converter 115 and an acoustic to electrical conversion device 155. In some embodiments, the acoustic-electric conversion device 155 can be disposed in the earphone housing to receive the noise signal V2(t) and convert it into an electronic signal E2(t). The analog to digital converter 115 is coupled to the acoustic-electrical conversion device 155 and converts the electronic signal E2(t) to the aforementioned digital noise signal C(n), wherein the digital noise signal C(n) can be used to estimate the noise signal V2 (t) The power of the corresponding digital signal (hereinafter referred to as noise signal V2(n)).

In some embodiments, the noise signal V2(n) can be used to estimate a signal component of the noise signal V(n) that is close to the frequency of the reference signal X(n) described later. Since the reference signal X(n) is usually set to a low frequency signal, and since the low frequency signal is relatively easy to penetrate the earphone casing, the signal strength of the noise signal V2(n) at a low frequency generally corresponds to the noise signal V. (n) At low frequency signal strength, in the subsequent embodiments, the signal strength of the noise signal V2(n) is used to compare the signal strength of the noise signal V(n).

In some embodiments, the voltage gain of the transfer function H1(z) is higher than the transfer function H2(z). In other words, the noise cancellation signal NC(n) generated by the transfer function H1(z) is greater than the noise cancellation signal generated by the transfer function H2(z). No. NC(n). Equivalently, filter 122 can have a better noise cancellation effect on filter 124 at any frequency. In general, the higher the voltage gain of the filter, the lower its stability. In other words, in this example, filter 124 has better stability than filter 122, but has a lower voltage gain. In some embodiments, filter 122 is selected when device 100 is in an on-ear state, and filter 124 is selected when device 100 is in an off-ear state.

In some techniques, in order for the headphone noise cancellation system to remain stable in the near-ear or off-earth state, a single filter with a lower voltage gain is used to improve system stability. However, in these techniques, the noise canceling system cannot be provided to provide a better noise canceling effect when the earphone is in the near ear state. Compared with the above technique, by analyzing the digital signal Y(n), the noise signal V2(n), the mixing signal U(n), and the reference signal X(n), the detecting circuit 140 can determine that the noise canceling device 100 is at Near ear or ear. In this way, in the near-ear state, the detecting circuit 140 can output the switching signal SE to select the filter 122, thereby improving the noise canceling effect. Alternatively, in the off-ear state, the detection circuit 140 can output the switching signal SE to select the filter 124 to maintain the stability of the system.

The reference signal generator 160 generates the reference signal X(n) to the arithmetic circuit 132. In some embodiments, the frequency of the reference signal X(n) is a frequency that is not perceptible by the human ear. For example, the frequency of the reference signal X(n) is about 10 Hz, but this is not limited to this case. In other embodiments, the reference signal X(n) may be periodically transmitted as shown in FIG. 4A, which will be described later.

In some embodiments, analyzing the noise canceling device 100 using Z-conversion, the following equation (1) can be derived: Where X(z) is the Z conversion of the reference signal X(n), Y(z) is the Z conversion of the digital signal Y(n), and V(z) is the Z conversion of the noise signal V(n), U(z) Is Z conversion of the mixing signal U(n), and S(z) is a transfer function between the electro-acoustic conversion device 136 to the acoustic-electric conversion device 150.

According to the above formula (1), when the power of the reference signal X(n) is much larger than the power of the noise signal V(n), the following equation (2) can be known: According to formula (2), under this condition, the ratio of Y(z) to U(z) is S(z), where S(z) may have different values because the earphone is near or ear. In some embodiments, S(z) will have a higher value in the near ear state. Conversely, in the ear state, S(z) will have a lower value. Therefore, the detecting circuit 140 can judge whether the noise canceling device 100 is currently in the near ear or the ear state by the ratio of Y(z) to U(z).

In addition, when the power of the reference signal X(n) is much smaller than the power of the noise signal V(n), the following equation (3) can be known: According to the above formula (3), under this condition, the ratio of Y(z) to U(z) is 1/H(z) instead of S(z). Therefore, when the detecting circuit 140 can judge whether the noise canceling device 100 has an unknown condition by the ratio of Y(z) to U(z).

Referring to FIG. 2, in operation S210, the detecting circuit 140 compares the ratio Px/Pn with the threshold TH1, wherein the ratio Px/Pn is the power Px of the reference signal X(n) to the power Pn of the noise signal V2(n). Ratio (as mentioned earlier, the signal strength of the noise signal V2(n) is used to compare the signal strength of the noise signal V(n)). If the ratio Px/Pn is greater than the threshold TH1, operation S220 is performed. If the ratio Px/Pn is lower than the threshold TH1, operation S215 is performed. In operation S215, the filter 124 is selected to provide a transfer function H2(z) to process the digital signal Y(n), thereby outputting the noise cancellation signal NC(n).

For example, if the ratio Px/Pn is lower than the threshold TH1, it means that the reference signal X(n) is much smaller than the noise signal V(n). Under this condition, the detecting circuit 140 determines that the aforementioned unknown condition occurs, and outputs the switching signal SE to select the filter 124. As a result, it is ensured that the noise canceling device 100 is maintained stable.

In operation S220, the detecting circuit 140 compares the ratio with the threshold TH2, wherein the ratio is expressed as Py/Pu, which is the ratio of the power Py of the digital signal Y(n) to the power Pu of the mixed signal U(n). If the ratio Py/Pu is higher than the threshold TH2, step S230 is performed. If the ratio Py/Pu is lower than the threshold TH2, step S215 is performed. In operation S230, the filter 122 is selected to provide a transfer function H1(z) to process the digital signal Y(n), thereby outputting the noise cancellation signal NC(n).

For example, if the ratio Py/Pu is higher than the threshold TH2, the value of the transfer function S(z) is higher. As mentioned previously, in the near ear state, S(z) will have a higher value. Therefore, under this condition, the detecting circuit 140 determines that the near-ear state is present, and outputs the switching signal SE to select the filter 122. As a result, the noise canceling effect of the noise canceling device 100 can be improved.

Alternatively, if the ratio Py/Pu is lower than the threshold TH2, it means that the value of the transfer function S(z) is low. As previously stated, S(z) will have a lower value in the de-eared state. Therefore, under this condition, the detecting circuit 140 determines that the earing state is present, and outputs the switching signal SE to select the filter 124. As a result, it is ensured that the noise canceling device 100 is maintained stable.

In some embodiments, the power Px and the power Pn are the power of the reference signal X(n) and the noise signal V2(n) at the frequency of the reference signal X(n), respectively. In some embodiments, the power Px, the power Pn, the power Py, and the power Pu are reference signals X(n), noise signals V2(n), digital signals Y(n), and mixed signals U(n), respectively, in the reference signal. The power at the frequency of X(n). Referring to FIG. 3, the detection circuit 140 includes a plurality of band frequency filters 301 to 303, a plurality of power estimation circuits 311 to 314, and a logic circuit 320.

Each of the plurality of band-band filters 301-303 provides a predetermined frequency band to process the corresponding one of the mixed signal U(n), the digital signal Y(n), and the digital noise signal C(n). For example, the band frequency filter 301 filters out the signal component of the frequency of the frequency of the non-reference signal X(n) in the mixed signal U(n) to output the signal U'(n). The band filter 302 filters out the signal component of the frequency of the digital signal Y(n) having the frequency of the non-reference signal X(n) to output the signal Y'(n). The band frequency filter 303 filters out the frequency of the non-reference signal X(n) in the digital noise signal C(n). The signal component of the frequency is output signal C'(n).

The power estimation circuit 311 calculates the power Pu of the signal U'(n). The power estimation circuit 312 calculates the power Py of the signal Y'(n). The power estimation circuit 313' calculates the power Pn of the noise signal C'(n). The power estimation circuit 314 calculates the power Px of the reference signal X(n).

In some embodiments, the plurality of power estimation circuits 311 314 314 can be implemented by a power detector. In some embodiments, the plurality of power estimation circuits 311-314 described above may be implemented by an arithmetic circuit that performs algorithms for various power calculations. The various implementations described above are merely examples, and the present invention is not limited thereto.

The logic circuit 320 determines the foregoing ratio Py/Pu and the ratio Px/Pn according to the plurality of powers Pu, Py, Pn, and Px to perform a plurality of operations of the method 200 to generate a corresponding switching signal SE. In some embodiments, logic circuit 320 can be implemented by various digital circuits, processing units, or microcontrollers.

Referring to FIGS. 4A and 4B, for easy understanding, similar elements to those of the preceding FIGS. 1 to 3 in FIGS. 4A to 4B will be designated by the same reference numerals.

In some embodiments, the noise cancellation device 100 can estimate the power Pn of the noise signal V(n) without the acoustoelectric conversion device 155 and the analog to digital converter 115. In this example, as shown in FIG. 4B, the reference signal X(n) is provided with an enable period T1 and an disable period T2. During the enable period T1, the reference signal X(n) generates a frequency that the aforementioned human ear cannot perceive. During the disable period T2, the amplitude of the reference signal X(n) is set to zero. According to the formula (1), in the inactive period T2, the following formula (4) can be known: Therefore, in this example, the detecting circuit 140 can calculate the power Pn of the noise signal V(n) according to Y(n) and Equation (4). In some embodiments, the transfer function S(z) in equation (4) can be set to have a larger value in the near-ear state and the de-eared state.

For example, as shown in FIG. 4A, the detection circuit 140 includes a plurality of band frequency filters 301 to 302, a plurality of power estimation circuits 311 to 313, and a logic circuit 320.

Compared with FIG. 3, in this example, the power estimation circuit 311 further determines the mixing signal U(n) according to the signal U'(n) in the enabling period T1 of the reference signal X(n). Power Pu at the frequency of X(n). The power estimation circuit 312 further determines the power Py of the digital signal Y(n) at the frequency of the reference signal X(n) according to the signal Y'(n) during the reference signal X(n) enable period T1, and is in the reference signal X. The disable period T2 of (n) determines the power Pn of the noise signal V(n) at the frequency of the reference signal X(n) according to the signal Y'(n) and the above equation (4). The power estimation circuit 313 further determines its power Px based on the reference signal X(n) during the enable period T1 of the reference signal X(n).

In some embodiments, the power estimation circuits 311 to 313 do not need to receive the reference signal X(n), but directly receive the clock signal corresponding to the enable period T1 and the disable period T2 of the reference signal X(n). For example, when the reference signal X(n) is in the enable period T1, its corresponding clock signal is 1 (or 0), and when the reference signal X(n) is in the disable period T2, its corresponding clock. The signal is 0 (or 1).

The circuit elements in the noise canceling device 100 in the above embodiments may be implemented by software, hardware, or a combination thereof. For example, components in the inverse noise filter circuit 120 and/or the detection circuit 140 can be implemented by digital signal processing.

In summary, the noise canceling device 100 and method provided by the present invention The 200 can be analyzed in different settings to measure the near ear state and the ear state to selectively employ appropriate filters to improve the performance of the audio processing system.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the case. Anyone who is familiar with the art can make various changes and refinements without departing from the spirit and scope of the case. Therefore, the scope of protection of this case is subject to the attached application. The scope defined by the patent scope shall prevail.

100‧‧‧Noise elimination device

110, 115‧‧‧ analog to digital converter

120‧‧‧Backward noise filter circuit

130‧‧‧Output circuit

140‧‧‧Detection circuit

150, 155‧‧‧Audioelectric conversion device

160‧‧‧Reference signal generator

SO(t)‧‧‧Sound output signal

V(t), V2(t)‧‧‧ noise signal

E1(t), E2(t)‧‧‧ electronic signals

Y(n)‧‧‧ digital signal

H1(z), H2(z)‧‧‧ transfer function

122, 124‧‧‧ filter

126‧‧‧Switching circuit

NC(n)‧‧‧ Noise Cancellation Signal

SE‧‧‧Switch signal

132‧‧‧Operating circuit

134‧‧‧Digital to analog converter

136‧‧‧Electrical sound conversion device

X(n)‧‧‧ reference signal

M(n)‧‧‧ input signal

U(n)‧‧‧mixing signal

C(n)‧‧‧ digital noise signal

S(z)‧‧‧ transfer function

Claims (10)

A noise canceling device comprising: a reverse noise filter circuit for providing one of a plurality of transfer functions to process a digital signal to generate a noise canceling signal, wherein the transfer functions are different from each other; and an output circuit And mixing the noise cancellation signal, a reference signal and an input signal to generate a mixed signal, and generating an audio output signal based on the mixed signal, wherein the digital signal is associated with the sound output signal; and detecting a circuit for controlling the reverse noise filter circuit to provide the corresponding one of the transfer functions according to a comparison result between a first ratio and a first threshold, wherein the first ratio is the mixed signal A ratio of a first power to a second power of the digital signal. The noise canceling apparatus of claim 1, wherein the transfer functions comprise a first transfer function and a second transfer function, a voltage gain of the first transfer function being higher than a voltage gain of the second transfer function, The back noise filter circuit provides the first transfer function when the first ratio is greater than the first threshold, and the reverse noise filter circuit provides the first when the first ratio is less than the first threshold Two transfer function. The noise cancellation device of claim 1, further comprising: a first analog to digital converter for converting a first electronic signal to The digital signal, wherein the first electronic signal is associated with the sound output signal and a noise signal. The noise canceling device of claim 3, wherein the detecting circuit is further configured to compare a second ratio with a second threshold to control the reverse noise filtering when the second ratio is less than the second threshold The second circuit is configured to provide the second transfer function, wherein the second ratio is a ratio of a third power of the reference signal to a fourth power of the noise signal, and the detecting circuit is further configured to use the second ratio greater than the The second threshold is compared to the first threshold and the first threshold. The noise canceling device of claim 4, wherein the detecting circuit comprises: a plurality of band-frequency filters for respectively processing the mixed signal, the digital signal and a digital noise signal, wherein the digital noise signal is used for Estimating the power of the noise signal; the plurality of power estimation circuits are configured to determine the first power according to the mixed signal, the processed reference signal, the processed digital signal, and the processed digital noise signal, The second power, the third power, and the fourth power; and a logic circuit configured to determine the first ratio according to the first power and the second power, and determine according to the third power and the fourth power The second ratio, wherein the logic circuit is further configured to compare the first ratio with the first threshold, and compare the second ratio with the second threshold to control the reverse noise Filter circuit. The noise canceling device of claim 5, further comprising: a second analog to digital converter for converting a second electronic signal to the digital noise signal. The noise canceling device of claim 6, further comprising: a first sound electricity conversion device for receiving the sound output signal and the noise signal and generating the first electronic signal; and a second sound electricity conversion device, For receiving the noise signal and generating the second electronic signal. The noise cancellation device of claim 4, wherein the reference signal has a uniform energy period and a disable period, the detection circuit includes: a plurality of band frequency filters for respectively processing the mixed signal and the digital signal a first power estimation circuit for determining the first power according to the processed reference signal during the enabling period; a second power estimating circuit for using the processed digital number during the enabling period The signal determines the second power, and determines the fourth power according to the processed digital signal during the disable period; a third power estimating circuit is configured to determine the third power according to the reference signal during the enabling period And a logic circuit, configured to determine the first ratio according to the first power and the second power, and determine the second ratio according to the third power and the fourth power, The logic circuit is further configured to compare the first ratio with the first threshold and compare the second ratio with the second threshold to control the reverse noise filter circuit. The noise canceling device of claim 1, wherein the output circuit comprises: an arithmetic circuit for mixing the noise canceling signal, the reference signal and the input signal to generate the mixed signal; a digital to analog converter, And converting the mixed signal to convert the mixed signal; and an electro-acoustic converting device for outputting the sound output signal according to the converted mixed signal. A noise canceling method includes: controlling a reverse noise filter circuit to provide a corresponding one of a plurality of transfer functions to process a digital signal to generate a noise canceling signal, wherein the transfer functions are different from each other; and mixing the noise canceling signal a reference signal and an input signal to generate a mixed signal, and output an audio output signal based on the mixed signal, wherein the digital signal is associated with the sound output signal; and according to a first ratio and a first threshold A comparison result controls the inverse noise filter circuit to provide the corresponding one of the transfer functions, wherein the first ratio is a ratio of a first power of the mixed signal to a second power of the digital signal.